High-field ODMR investigation of the EL2 defect in semi-insulating GaAs

摘要

The microscopic structure of the EL2 defect in semi-insulating GaAs has remained controversial. It is generally agreed that EL2 is an As antisite-related defect, but whether it is an isolated ASG, defect or an AS(Ga)-related pair defect, has not been unambiguously decided. In a previous investigation with electron nuclear double resonance (ENDOR) detected via the magnetic circular dichroism (MCD) of the near infrared absorption of EL2(+) (MCDA-ENDOR) at 24 GHz (K-band) the local symmetry could not be determined conclusively due to complicated multiple ENDOR line splittings caused by strong effects of pseudo-dipolar couplings. We report on an MCDA-ENDOR investigation at 95 GHz (W-band) where the undesired 15 As ENDOR line splittings due to pseudo-dipolar coupling were suppressed. The surprising result is that the angular dependence of the nearest 15 As shell shows almost T-d symmetry. A small non-equivalence of the nearest neighbours is hidden in an unresolved ENDOR line width for B-0[0 0 1] and can be a most 1.5% of the superhyperfine (shf) constants. The lines of a further As-75 shell, interpreted as the fifth shell, are split into at least two subshells indicating a pair defect in spite of the almost equivalence of the nearest neighbours. It is discussed whether EL2 is an As-Ga(+)-V3-Ga Ga pair defect following recent theoretical calculations showing that this pair defect has the observed properties of the shf interactions. (C) 2003 Elsevier B.V. All rights reserved. [References: 11]